1975 CJ5 8-304 Exhaust Backfire when Warm - Jeep Wrangler Forum
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Old 11-15-2017, 07:08 PM
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1975 CJ5 8-304 Exhaust Backfire when Warm

I've been trying to find some help on my own and finally decided to ask the experts!

Recently - my 1975 CJ5 AMC 304 Manual started running really rough, mis-firing, and back-firing once it gets warmed up.

My researched seemed to point to perhaps something with the EGR either failing - leaking - or something like that. I was also encouraged to check that there were no vacuum leaks around the carb. Here is what I've done:

1. Bought some starter fluid and sprayed it around the carb while it was running to monitor for the engine rev'ing up b/c of a leak. There seemed to perhaps be some evidence of that - but I couldn't nail the location down to anything specific. I did notice that the air filter seal is "less than perfect".

2. Check that all tubes are connected correctly for the EGR - CTO - and such. What I found was that:
- There are no tubes going to the EGR from the CTO
- There is no tube going to the carb from the CTO
- There is one tube on the CTO going to the intake on the air filter

What the heck does all of that mean???? And...is the possibly the issue? If so - why is it just showing up now? Is this EGR business something that needs to be remedied regarless?

Any Ideas???? Any help would be greatly appreciated.

/Jeff DeVerter

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Old 12-08-2017, 08:08 AM   #2
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Originally Posted by jdeverter View Post
I've been trying to find some help on my own and finally decided to ask the experts!

Recently - my 1975 CJ5 AMC 304 Manual started running really rough, mis-firing, and back-firing once it gets warmed up.

My researched seemed to point to perhaps something with the EGR either failing - leaking - or something like that. I was also encouraged to check that there were no vacuum leaks around the carb. Here is what I've done:

1. Bought some starter fluid and sprayed it around the carb while it was running to monitor for the engine rev'ing up b/c of a leak. There seemed to perhaps be some evidence of that - but I couldn't nail the location down to anything specific. I did notice that the air filter seal is "less than perfect".

2. Check that all tubes are connected correctly for the EGR - CTO - and such. What I found was that:
- There are no tubes going to the EGR from the CTO
- There is no tube going to the carb from the CTO
- There is one tube on the CTO going to the intake on the air filter

What the heck does all of that mean???? And...is the possibly the issue? If so - why is it just showing up now? Is this EGR business something that needs to be remedied regarless?

Any Ideas???? Any help would be greatly appreciated.

/Jeff DeVerter
Yours Jets or secondaries may be clogged or corroded because of the ethanol in the gas. Id take the entire carb apart and clean it up with some brake clean and a brush then re-assemble.

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Old 12-19-2017, 08:04 PM   #3
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I think the EGR gas goes in under the carb on some 304's and that plate can burn out inside and cause what you have, I had a 75 Mustang 351 that burned out the plate under the carb. and did just what you have, Good Luck!
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